Variable inductor



March 14,1944. J, P, PUTNAM 2,343,999

VARIABLE INDUGTOR Filed March 19, 1942 vw -1 H w Patented Maf. 14, 1944 UNITED sTATEs PATENT o1-Fica` VARIABLE rmmc'roa .101m P.A Putnam, Boston, Mass., signor to The .Reece Button Hole Machine Company, Boston,

Mass., a corporation of Maine Application March 19, 1942, Serial No. 435,286

This invention relates to variable inductors 6 Claims.

which are particularly adapted, though not limited to tuning units for radio receivers of the all wave type.

In my prior Patent 2,201,453 issued May 21, 1940, there is disclosed a variable inductor whose inductively related coils are mounted on relatively rotatable elements of ferro-magnetic mamay be held in spaced relation by any suitable means, such as cross bars (not shown). More particularly, the supportA i carries at one end a terial which form a substantially closed mag- I netic held. The inductance range of this inductor is so large that the same, when used in conjunction with a suitable variable condenser, is well able to cover the entire short wave broadcast range, the intermediate range for police and aviation broadcasts, and the American broadcast range. The Q or figure of merit of this inductor is also sufilciently high to obtain fair image rejection, fair selectivity and a fair signal to noise ratio in a radio receiver.

It is the object of the presentinvention to increase the Q or ilgure of merit of this inductor so as to considerably improve therimage rejection and the selectivity of a radio receiver, and to better the signal to noise ratio and thereby obtain a higher stage gain. f

This object is accomplishedby spacing the inductively related coils from their respective ferro-magnetic supportingvr elements and thereby reduce the capacity between them. By way of example, this may be d'one Aby providing spacers or liners of any suitable insulating material between the coils and their' respective ferro-magnetic elements, whereby'y the thickness of the insulating spacers is so selected as to effect the optimum compromise between a high "Q and a large inductive range.

-The foregoing and other objects of the invention, together with means whereby the latter may be carried into eiect will best be understood from the following description of an illustrative embodiment shown in the accompanying drawing: in which,

Fig. l is an enlarged cross-section through an inductor embodying the present invention.

Fig. 2 is a perspective view oi the inductor.

Fig. 3 is a perspective view of certain separated parts of the inductor. The inductor disclosed in the drawing isc the same general construction as the inductor disclosed in my above-referred Patent No.

v3,201,453. Accordingly, there is provided a substantially U-shaped support i'of any suitable insulating material which carries a variable inductor l2: The support lllv is rotatably mounted between metallic end plates 14a and |411 which disc I6 which provides one race |8`of a ball bearing 20 whose other race 22 is provided by the adjacent end plate |4a. The other end of the support l0 is provided with a shank 24 which is journalled in an opening 25 in the other end plate l4b. The shank 24 is provided with a central depression 26 in which is retained by a strip 21 a steel ball 28 that acts as a thrust bearing. The disc I6 is provided with a shank 30 which projects through an opening 3| in the end plate 14a and ycarries a knob (not shown) with which to rotate the support I0 about the axis :1J-x (Fig. l).

The inductor I2 consists of a rotor 32 and a stator 34. The rotor 32 comprises a ferro-magnetic shell 36 and a coil 31 which is carried by said shell through intermediation of a spacer or liner 38 of any suitable insulating material. The stator 34 comprises a ferro-magnetic core 33 and a coil 40 which is carried by said core through intermediation of a spacer or liner 4I of any suitable insulating material. More particularly, the rotor shell 3B consists of two separate halves or members 36a and 36h of which the member 36h is located in a correspondingly shaped recess' 45 in the yoke 41 of the support i0. The shell members 36a and 36h are secured to each other as well as to the support ill by means of a plurality of bolts 46 and nuts 49 in the manner shown in Fig. 1. The shell members 36a and 36h are v48 is furthermore provided with a wide annular groove 50 in which the insulating liner 38 reposes in the manner shown in Fig. 1. The liner 38 is also preferably formed of two complementary halves 38a and 38h (Fig. 3). The rotor coil 31 is preferably made of two separate, space-wound coil parts 31a and 3117 (Fig. 3) which are mounted in the liner halves 38a and 38h, respectively, in any suitable manner, such as by cementing. These coil parts are then connected in series by connecting their adjacent leads 54 in the manner indicated in Fig. 3. The opposite leads 53 of the rotor coil 31 are passed to the outside ci the rotor shell 36 through suitable holes 53 in the latter.

Mounted for rotation about the axis :c-x (Fig. 1) in complementary bearing surfaces 60 and 62 of the liner halves 38a and 38h, respectively, are

axially alined metallic stubs U4 which proiect from the stator 8l. More particularly, these stubs I( are mounted in one of two parts of which the stator liner ll is composed and which are slipped over the ferro-magnetic core l! and preferably cemented together at their abutting surfaces. The stator coil 4l is preferably made of two separate. space-wound coil parts a and b which are suitably secured, as by cementing, to the liner 4I. These coil parts are then connected in series by connecting their adjacent leads 6l in the manner indicated in Fig. 1.

Mounted on the opposite ends of the metallic, and hence conductive, journal stubs I4 of the stator Il are non-inductively wound, flexible spiral connectors 1I and 12 of the type disclosed in my prior Patent No. 2,097,642, issued November 2, 1937. As best shown in Fig. 1, the opposite ends 1I of the stator coil 4U are connected with the spiral connectors 1l and 12 by way of conductors 1l in narrow grooves 1l in the stator liner 4|, metallic screws 11 which hold the stubs Il in said liner, and the stubs Il themselves. Likewise, the opposite leads I8 of the rotor coil l1 are connected with the spiral connectors 1I and 12. More particularly, one of these leads I8 is connected with the spiral connector 1l through intermediation of a conductor 1l, while the other lead is connected withthe spiral connector 12 by way of one of the metallic bolts ll and suitable conductors Il and I2. Hence, the rotor coil I1 and the stator coil I0 are connected in parallel across the spiral connectors 1I and 12. It is to be understood, however, that these coils I1 and Il may be connected in series with each other if desired.

To prevent rotation o! the stator 34, metallic rods Il and Il are secured to the stubs ll and passed through holes l! in a cross bar Il of any suitable insulating material which is secured to the Opposite end plates Ila and "bin any suitable maner, as by screws II. Thus, the stator 3l will remain stationary and the support Il as weil as the rotor l2 thereon may be rotated relative to the stator. The metallic rods Il and Il may be conveniently used as terminals for connecting the inductor in an electrical circuit.

The stator core Il and the shell members Ila and lib are preferably molded under pressure from iinely divided iron` particles and a suitable binder. ,The ferro-magnetic stator core 3l and the ferro-magnetic rotor shell IB form together lil. magnetic path which is closed except forthe narrow and substantially spherical gap between them. Hence, a maximum ux linkage between the relatively rotatable coils 31 and Il is attained when the latter are in the position of maximum coupling. '111e result thereof for this posion of the coils is a high maximum inductanoe for the inductor. However, when the coils 31 and I are in the position of maximum opposition and minimum inductance, the ferromagnetic stator core and 4the ferro-magnetic rotor shell are substantially without effect upon the inductance. By reason of the foregoing, the inductance ratio of the present inductor is unusually large. liest inductors as herein described have been built to obtain an inductance ratio of 16 to 1.

In spacing the inductively related coils 31 and Il from their respective ferro-magnetic supports Il and 30 by interposing the spacers or liners 38 and Il between them, the capacity between these coils and their ferro-magneti supports is greatly reduced, whereby the thickness of the insulating spacers is so selected as to effect the optimum compromise between a high "Q and a large inductive range.

A tuning condenser may be combined into one unit with the present inductor in the manner disclosed in my prior Patent No. 2,066,944, issued January 5, 1937, in which case the support 10 is provided with s'paced lugs Ill for supporting cross bars |02 on which the rotor plates l of the condenser are stacked in the manner shown in Fig. 2,

I claim:

1. A variable inductor comprising, in combination, two relatively rotatable ferro-magnetic members spaced from each other by a gap in any angular relative position of said members: conductively connected and inductively related coils in said gap; and meansmounting said coils on said members, respectively, in spaced relation therefrom so that said coils are closer to each other than to their respective members. thereby considerably increasing the figure oi merit of the inductor.

2. A variable inductor comprising, in combination, two relatively rotatable ferro-magnetic members of which one is substantially enclosed within the other and spaced therefrom by a gap in any angular relative position of said members; conductively connected and inductively related coils in said gap; and means mounting said coils on said members, respectively, in spaced relation therefrom so that said coils are closer to each other than to their respective members, thereby considerably increasing the figure of merit of the inductor.

3. .A variable inductor comprising, in combination, two relatively rotatable ferro-magnetic members of which one is substantially enclosed within the other and spaced'therefrom by a gap in any angular relative position of said members: insulating liners in said gap mounted on the adjacent surfaces, respectively, of said members; and conductively connected and inductively related coils in said gap mounted on said liners, respectively, said liners being of such thickness as to space said coils farther from their respective members than from each other, thereby considerably increasing the figure of merit of the in ductor.

4. A variable inductor comprising, in combination, two relatively rotatable ferro-magnetic members of which one is substantially enclosed within the other and spaced therefrom by a gap: insulating linersin said gap mounted on the adjacent surfaces, respectively, of said members and spaced from each other by a spherical gap of uniform width in any relative angular position of said members; and conductively connected and inductively related, spherical coils in said spherical gap mounted on said liners, respectively, said liners being of such thickness as to space said coils farther from their respective members than from each other, thereby considerably increasing the figure of merit of the inductor.

5. A variable inductor comprising, in combination, a ferro-magnetic shell member; a ferromagnetic core member in said shell member; insulating liners on the adjacent surfaces, respectively, of said members; coils mounted on said liners, respectively, in inductive relation with -each other; and means for conductively connecting said coils including opposite metallic stubs projecting from said core member to the outside of seid shell member and being iournalled' tively, oi said members; coils mounted on said liners, respectively, in inductive relation with eachother; and means for conductively connecting said coils including opposite metallic stubs mounted in the liner of said core member and projecting `to the outside of the said shell membei', said stubs being Journalled in the liner of said shell member and the latter member being provided with apertures through which said stubs pass with clearance, and said liners being of such thickness as to space said coils farther from l0 their respective members than from each other,

thereby considerably increasing the iigure of merit oi' the Inductor.

JOHN P. PUTNAM. 

